1. Field of the Invention
The present invention relates to a powder conveying device.
2. Related Background Art
Conventionally, a screw is used as the device for conveying a powder, for example to convey the powder inside a pipe by rotating the screw provided within the pipe. Such a powder conveying device is frequently used as the device for conveying a toner from a toner hopper to a developing machine.
However, as the screw within the pipe must be rotated by a motor in the above conventional example, a problem exists in that the consumption power increases, and the sound of rotation might be relatively larger. Also, because of the constitution requiring the relatively complex screw and the motor, a larger space is necessary and the cost is increased.
If the clearance between an inner wall of pipe and the screw is large, the conveying efficiency is decreased. Conversely, if the clearance between the inner wall of pipe and the screw is small, the conveying efficiency is raised, but there us a problem in that the rotational torque of screw might be larger with the friction between the screw and the inner wall of pipe.
Furthermore, the powder may be degraded or broken due to the friction between the inner wall and the screw, or melt with the frictional heat. Generally, the powder can be easily charged with the friction, so that the powder is charged due to the friction with the screw during the conveyance, thereby sticking to the screw, and resulting in a problem that a conveyance failure may arise in severe cases.
Also, a conveying device is well known in which a large particle-like body is laid on a greatly vibrating diaphragm, inclined obliquely downward, to help it slide down such a slant plane with the oscillation. However, there is a disadvantage in that a large energy is necessary to cause the large oscillation of diaphragm, or a large oscillation sound might be generated.
Also, there is a device in which a fine particle-like body is conveyed by applying an air flow thereon or conveyed along with the air flow by entraining the powder into the air flow. However, such a device has a lower conveyance density of fine particle-like body due to the air fed in, resulting in a low efficiency conveying device.
Furthermore, in the field of a developing machine for developing an electrostatic latent image, there is widely used means for attaching electrostatically a charged toner (colored fine powder) to a carrying member such as a rotating roller and conveying the toner along with the rotation of the carrying member.
However, the charge polarity and amount of toner particle are variously changed, or the absolute quantity is easily varied and unstable, so that the density, gradation and line image reproducibility are unstable. Also, the quantity of particles sticking to the carrying member electrostatically is varied with the charge amount of the toner particle. That is, the humidity is changed, thereby varying the quantity of charged fine toner particles (thickness of toner layer) conveyed sticking electrostatically to the carrying member moving at constant speed, so that there is a disadvantage in that the quality of the image might be degraded.
Furthermore, conventionally, no mechanical driving portion could be eliminated, as resultant troubles easily arise due to the abrasion or oscillation load variation in this mechanical driving portion.